The purpose of this proposal is to implement phosphate triester tether methods for the synthesis of complex biologically relevant natural products. We have provided empirical evidence that counters historical and traditional views associated with the utilization of phosphates in synthesis. The logic of implementing phosphate-tethers is predicated in a number of salient features inherent to phosphorus, including: (i) facile multivalent coupling pathways (ii) chirality at phosphorus, (iii) multivalent activation to corresponding carbinol centers via innate leaving group ability within the phosphate tether, (iv) an orthogonal stability/reactivity profile that imparts protecting group features, and (v) inherent nucleophilic characteristics in pendant phosphate esters/acids that enable iodophosphonylation protocols. The proposed method will serve as the cornerstone in the asymmetric synthesis of (1) cytostatin, which is known to inhibit cell adhesion to the extra-cellular matrix by selectively inhibiting protein phosphatase 2A and has been shown to prevent metastasis, inhibit tumor cell growth, inhibit cell adhesion and cause apoptosis in certain cell lines;(2) leustroducsin B (LSN-B), which has shown antitumor activity and has potential as a novel hematopoietic growth factor (HGF) with application to a number of hematopoietic diseases;(3) fostriecin, a potent phosphatase inhibitor that displays in vitro activity against a broad range of cancerous cell lines including lung cancer, breast cancer, and ovarian cancer, as well as in vivo antitumor activity;(4) dolabelides A and B which are a family of recently isolated 22- and 24-membered macrolides that exhibit promising cytotoxicity properties against HeLaSa cells and (5) Iso-migrastatin, a natural product isolated from Streptomyces platens is and a member of the migrastatin family. Migrastatin is a shunt metabolite of iso-migrastatin and has been found to be a potent tumor cell migration inhibitor. The development of this innovative approach represents an integrated platform for the emergence of a new and powerful tether for small molecule synthesis. Overall, the phosphate tether will serve a multi- faceted role as a coupling agent, protecting group, latent leaving group and pendant nucleophile providing multivalent activation and ultimately dictating selective cleavage reactions within several bicyclic and monocyclic phosphate triesters.